Fast, uniform, and large scale heat treatment by plasma-based electrons

Heat treatment of steels by electron beams with an energy density ranging from 1 to 10 kW/cm2 results in a considerable hardness improvement and wear reduction. Hence, electron beam treatment is a typical line-of-sight process and demands a complicated target manipulation and beam rastering system.
A new method is presented, circumventing the limitations inherent in the scanning electron beam treatment. The workpiece to be treated is immersed into a plasma and surrounded by a negatively biased grid, preventing the penetration of plasma electrons. Further the workpiece is connected to a positive DC high voltage source of about 20 kV and a capacitor, acting as an energy storage. Changing the grid bias, electrons are extracted from the plasma and accelerated by the positive potential towards the workpiece. During the pulsed electron bombardment power densities of about 10 kW/cm2 can be achieved resulting in a rapid thermal heating and self quenching, occurring after the electron pulse. Detailed investigations are presented on the response of a plasma if electrons are extracted by a large electrode with special emphasis on the processes near the wall and near the control grid.